A DESCRIPTION OF THE GENUS DIMETRODON, COPE. 15 



lumbar vertebrae, which, form the dorsal fin seen in other species of the genus. In this 

 species the spine sends off, a short distance above the neural canal, a pair of opposite 

 short branches, forming a cross. At various more elevated positions there are given off 

 tuberosities, which alternate with each other." This species of Dimetrodon was later made 

 the type of Naosaurus Cope. 



Cope's "Second Contribution to the History of the Vertebrata of the Permian For- 

 mation of Texas " 10 appeared June 5, 1880. The general conclusions about the Thero- 

 morpha he had already published in the American Naturalist, December, 1878, which 

 we have reviewed above. Cope now believes that the Pelycosauria are related to the 

 Amphibia in some important respects (scapular and pelvic arches, humerus, dentition 

 of palatal region), but he says : " In spite of these approximations, the Pelycosauria are 

 distinctly reptilian in their single occij)ital condyle, ossification of the basi-cranial axis 

 and single vomer." 



" Thus the reptiles and batrachia of the Permian period resemble each other and 

 the Mammalia more closely than do the corresponding existing forms." 



The genus Theropleura is more fully defined from a better preserved specimen of 

 Theropleura uniformis than 'any so far obtained. " The teeth are generally similar to 

 those of Clepsydrops and Dimetrodon, having compressed crowns with fore and aft cut- 

 ting edges. The incisors are distinguished by the presence of a diastema. Posteriorly 

 to this the teeth increase in size and then diminish ; one tooth near the middle of the 

 series is the largest, but does not in this species very much exceed the others. There is 

 at least one large incisor tooth. The bones of the head are smooth and not sculptured. 

 The symphysis of the mandible is short." The neural arches are distinct from the cen- 

 tra. Intercentra are said to be absent in the thirteen vertebrae preserved ; but there 

 was probably one below the centrum of the atlas. The ribs are two-headed, the capitu- 

 lar process extending downwards to the anterior border of the centrum. The neural 

 spines of some of the vertebrae are greatly elevated, as in the species of Clepsydrops and 

 Dimetrodon. Dermal rods are said to be present, suspected to be abdominal, and this is 

 considered a batrachian character. The neural spine of the axis is extended fore and 

 aft. The odontoid is distinct and is of large size. It has lateral and inferior articular 

 surfaces. 



Theropleura uniformis is described to be of the size of the larger Varanidw, and about 

 equal to the Clepsydrops natalis. It is characterized by a long and acuminate head, with 

 a large lateral nostril on each side, well forwards and approaching near the border of the 

 diastema. Anterior to the large lateral tooth there are nine teeth ; posterior to it there 

 are eighteen. Length of alveolar edge of mandible 0.120 m. 



A new species of Theropleura is described as T obtusidens, represented by nearly 



